Beam delivery system

ABSTRACT

A photon energy beam delivery system has a gas delivery tube extending generally the length of the beam path, having a plurality of openings oriented generally toward the beam path. Gas is discharged through the openings, flowing proximal to the beam path, resulting in the desired gas movement within the beam path throughout a sufficient length of the beam path, thereby reducing, eliminating or minimizing degradation of the beam.

This application is a divisional of U.S. application Ser. No.09/344,772, filed Jun. 28, 1999, now U.S. Pat. No. 6,331,693, which ishereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to photon beam delivery systems,and is particularly directed to a system which eliminates or reducesdegradation of a photon energy beam providing a consistent andsymmetrical power distribution for the length of a photon energy beam.The invention will be specifically disclosed in connection with anindustrial laser cutter having an enclosed beam delivery system.

BACKGROUND OF THE INVENTION

The use of photon energy beams is well known. Photon energy beams can beused for a variety of purposes, ranging for example from thetransmission of signals and information to the cutting of material, suchas the use of lasers to cut sheet metal. At least when used for cutting,it typically is desirable for the photon energy beam to have a radiallysymmetrical power distribution which is constant along the length of thebeam. However, in some instances the power distribution of the photonenergy beam, when it reaches its target, is not consistent andsymmetrical. An asymmetric power distribution reduces the efficiency ofthe photon energy beam. Such a non-consistent and asymmetric powerdistribution is particularly troublesome when the beam is used to cutmaterial.

The initial quality of a photon energy beam is dependant on theresonator which generates the beam. It is widely acknowledged that thegas through which a photon energy beam propagates in a photon beamdelivery system can adversely affect the beam. In systems in which thelength of the beam path through the gas varies, such as in laser cutterswith moving optics, the beam quality frequently degrades as the beampath increases. Degradation in beam quality, between the resonator andthe beam's target, is often attributed to contaminants and impurities ofthe gas within the photon beam delivery system in the beam path,affecting characteristics such as the beam quality K factor and thedivergence.

In non-sealed beam delivery systems, it is known to provide a purgesystem which introduces a flow of very clean, dry purge gas, such as airor nitrogen, into an enclosure surrounding the beam, creating a positivepressure within the enclosure. Since the enclosure is not sealed, thepositive pressure guarantees that gas will flow from the interior of theenclosure to the ambient environment to prevent ambient contaminants andimpurities from entering the enclosure. However, such positive pressuresystems are not necessarily 100% effective at keeping contaminants andimpurities out. For example, photon beam delivery systems on lasercutters typically use bellows to enclose the beam. During rapidmovements of the gantry carrying the nozzle and beam delivery system,ambient air carrying impurities and contaminants can be pumped into theenclosure by the expansion and contraction of the bellows despite theuse of a purge system.

It has been suggested that the presence of CO₂ in the beam path is thesource of beam propagation degradation. Although CO₂ scrubbers areavailable, they are more expensive than the typical air cleaners.Additionally, even if CO₂ is removed from the gas introduced by a purgesystem, ambient impurities and contaminants may still be present withinthe enclosure of a non-sealed beam delivery system.

There is a need in the art for a beam delivery system which eliminates,reduces or minimizes degradation of the photon energy beam along thelength of the beam path, delivering to the target a beam havingsubstantially the same beam quality as generated by the resonator. Thereis a need in the art for a beam delivery system which delivers the samebeam quality regardless of the length of the beam path.

SUMMARY OF THE INVENTION

It is an object of this invention to obviate the above-describedproblems and shortcomings of the prior art heretofore available.

It is another object of the present invention to provide a beam deliverysystem which eliminates, reduces or minimizes degradation of a photonenergy along the beam path.

It is yet another object of the present invention to provide a beamdelivery system which delivers a beam to its target which is radiallysymmetrical.

It is still another object of the present invention to provide a beamdelivery system which provides a power distribution which is constantalong the length of the beam path without significant cost.

It is another object of the present invention to provide a beam deliverysystem which delivers a beam having consistent quality throughout therange of beam path lengths.

It is yet another object of the present invention to provide a beamdelivery system which prevents or reduces thermal or density gradientsproximal to the beam path.

It is another object of the present invention to provide a beam deliverysystem which can be used without specific gases or gas conditioning.

It is still another object of the present invention to provide a beamdelivery system which delivers gas uniformly or at discrete points alongthe beam path.

Additional objects, advantages and other novel features of the inventionwill be set forth in part in the description that follows and in partwill become apparent to those skilled in the art upon examination of thefollowing or may be learned with the practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

To achieve the foregoing and other objects, and in accordance with thepurposes of the present invention as described herein, there is provideda beam delivery system with a gas delivery tube extending generally thelength of the beam path, having a plurality of openings oriented towardthe beam path. Gas is discharged through the openings, flowing proximalto the beam path.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a perspective view of a laser cutter.

FIG. 2 is a fragmentary, diagrammatic plan view of a beam deliverysystem used with the laser cutter of FIG. 1.

FIG. 3 is a diagrammatic perspective view of the beam delivery system.

FIGS. 4A-D are power distribution profiles.

FIG. 5 is a cross sectional view taken at the location of line 5—5 ofFIG. 2.

FIG. 6 is an enlarged cross sectional view of the gas distribution tubeshown in FIG. 5.

FIG. 7 is a diagrammatic side view of the gas distribution tube of FIGS.5 and 6.

FIG. 8 is a cross sectional view taken at the location of line 8—8 ofFIG. 2.

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in detail, wherein like numerals indicatethe same elements throughout the views, FIG. 1 is a perspective view ofa laser cutter 2, such as the CL-707 sold by Cincinnati Incorporated,the assignee of this patent. Laser cutter 2 has a moving optics systemin which the material remains stationary as the laser beam cuts thematerial. Laser cutter 2 includes main frame 3, support member 4 whichis parallel to the X axis and gantry 5. Gantry 5 is moveably supportedat either end by tracks 3 a and 3 b of main frame 3. A pair of supporttubes 6 a, 6 b (FIG. 8), which are parallel to the Y axis, are supportedat either end by gantry 5.

Referring also to FIG. 2 which is a fragmentary, diagrammatic plan viewof the beam delivery system used with the laser cutter of FIG. 1, andFIG. 3 which is a diagrammatic perspective view of the beam deliverysystem, beam delivery system is generally indicated at 8. A beamdelivery system directs the photon energy beam from one location toanother, referred to herein as a target, such as material to be cut fora laser cutter. As is typical for laser cutting equipment, beam deliverysystem 8 directs laser beam 10 from resonator 12 to laser head 14. Laserbeam 10 is directed by mirrors 16 along X axis 18, Y axis 20, and Z axis22, through focal lens 24 to nozzle tip 26. Bellows 28 a-28 d surroundthe path of laser beam 10 and encloses beam delivery system 8. Bellows28 a and 28 b extend from a respective end of support member 4 (notvisible in FIGS. 2 and 3) to mirror housing 30, which reciprocates alongX axis 18. The mirror carried by mirror housing 30 directs laser beam 10from X axis 18 to Y axis 20. Bellows 28 c extends from mirror housing 30to mirror housing 32 and bellows 28 d extends from mirror housing 32 tothe end of tubes 6 a, 6 b. In the depicted embodiment, although bellows28 a-28 d are made from non-porous fabric, the seams can develop leaksdue to flexing fatigue. Mirror housing 32 reciprocates along Y axis 20,supports focal lens 24 and nozzle tip 26, and carries the mirror whichdirects laser beam 10 from Y axis 20 to Z axis 22.

As discussed above, it is desirable for the photon energy beam to have aradially symmetrical power distribution which is constant along thelength of the beam. The initial quality of the beam is dependant on theresonator: The beam delivery system does not improve the quality of thebeam. The resonator is selected based on the beam desired. Generally,for laser cutting, a Gaussian beam (TEM00), depicted in FIG. 4A, or aTEM01*, depicted in FIG. 4B, are desired. The goal of a beam deliverysystem of the present invention is to reduce as much as possible,preferably eliminating or minimizing, any degradation of beam qualitybetween the resonator and the target. FIGS. 4C and 4D illustrateexemplary asymmetrical power distributions that have been degradedthrough use of a prior art beam delivery system.

In the beam delivery system of the present invention, a gas distributiontube is used to distribute air along all or part of the length of thelaser beam path. It is noted that Is although in the embodiment depictedherein, dried and filtered air (produced by a Balston #75-20-L101, witha dew point temperature of about −20° Celsius) was used as the gasthrough which the beam was propagated, any suitable gas may be used. Inthe practice of this invention, even moist, non-filtered air may beused. However, it is noted that while it is functional to provide theturbulation adjacent the beam path, moist, non-filtered air is not verypractical as it may contaminate components of the beam delivery system,such as mirrors or lenses, and interfere with the operation.

Referring to FIG. 5, which is a cross sectional view of beam deliverysystem 8 taken at the location of line 5—5 of FIG. 2, bellows 28 asurrounds and is generally supported along its length by support member4 (although contact between bellows 28 a and support member 4 is notshown in FIG. 5). Laser beam 10 follows beam path 10 a located generallynear the center of support member 4. Gas distribution tube 32 is shownadjacent beam path 10 a, supported by the bottom surface 4 a of supportmember 4 and extending the length of X axis 18. Gas distribution tube 32has a plurality of openings 32 a generally aimed toward beam path 10 a.Gas distribution tube 32 is held in place in any conventional way.

In the embodiment illustrated, gas distribution tube 32 is a 0.219inches ID copper tube connected at one end to a source of pressurizedair (not shown) and sealed at the other end. Openings 32 a have adiameter of 0.032 inches and are spaced 12 inches apart. As shown inFIGS. 5 and 6, which is an enlarged cross sectional view of gasdistribution tube 32, gas distribution tube 32 is not located directlybelow beam path 10 a, but is disposed to one side such that angle α is10°±5°.

FIG. 7 is a diagrammatic side view of gas distribution tube 32illustrating the discharge of discrete air flows 34 of air into beampath 10 a. In one embodiment, air is supplied to a CL-707 laser with aRofin DC 025 2500 watt CO₂ slab laser, at 350 SCFH, 30 PSIG, and −20° C.dew point. Approximately 250 SCFH was delivered to the X axis gasdistribution tube and approximately 75 SCFH was delivered to the Y axisgas distribution tube. The volume of air depends primarily on the lengthof the beam path, as well as the size and leak rate of the enclosure, ifany. For a CL-707, a range of 300 to 600 SCFH at 20-35 PSIG has beenused. While not yet tested, lower pressures and flow rates may alsoproduce acceptable results.

As mentioned above, the area enclosed by bellows 28 a-28 d is not airtight, which allows the air to flow out of gas discharge tube 32 intobeam path 10 a and along the axes more freely. It is believed that thereduction, elimination or minimization of beam degradation results fromthe prevention or reduction in thermal and/or density gradients in thegas at or adjacent the beam path, as well as the prevention or reductionof stagnated gas at the beam path. The amount of air flow directed atand/or turbulence created at the beam path along at least a portion ofthe beam path length is selected so as to produce the desiredimprovement in beam degradation.

There are many alternatives to the location and type of gas distributiontube 32. An important function of gas distribution tube 32 is todistribute gas flow proximal beam path 10 a to reduce, eliminate orminimize any degradation of the photon energy beam, to provide aconsistent power distribution for the length of the beam path,approaching and preferably achieving the initial beam quality. Gasdistribution tube 32 could be mounted to any of the sides of supportmember 4. Any structure which can distribute-gas along its length,whether discretely or due to uniform porosity, can be used. For example,in one embodiment, a polyethylene tube was used. In such case, the tubewas secured in place by tape, such as HVAC tape, and slits cut with anExacto™ knife in the tube side after installation, which simplifiedproper orientation of the openings 32 a toward the beam path 10 a. Anymaterial may be used for gas distribution tube 32 as long as it does notinterfere with the beam propagation. Materials which release gases thatinterfere with beam propagation, such as rubber, should be avoided. Apassageway which is uniformly porous, such as a tube made of a non-wovenmaterial, with sufficient internal pressure may also work.

FIG. 8, which is a cross sectional view taken at the location of line8—8 of FIG. 2, illustrates bellows 28 c generally supported by supporttubes 6 a and 6 b. Support tube 6 a includes a plurality of openings 36generally aimed toward beam path 10 a. The interior of support tube 6 ais connected to a source of pressurized air (not shown) in anyconventional manner, such as through a fitting through the wall ofsupport tube 6 a. Any alternative structure capable of delivering airproximal to beam path 10 a may be used, such as a separate tube,although the use of support tube 6 a is convenient as it is alreadypresent.

Although the present embodiment specifically illustrates the gas beingdischarged transverse, and in particularly generally perpendicular, tobeam path 20 a, other directions may be used so long as a sufficientamount of air flow is produced proximal to beam path 10 a to produce thedesired gas movement within the beam path sufficient to reduce,eliminate or minimize degradation of beam quality. The gas flow does nothave to be strictly transverse, although the required gas flow increaseswith a decrease in the angle between the air flow and the beam path andwith distance from the beam path.

Gas flow may be introduced proximal to the beam path by the axialintroduction of an amount of gas sufficient to produce the desired gasmovement within the beam path throughout a sufficient length of the beampath. However, axial flow introduced at a single location, such asadjacent the resonator, will require a significant flow rate in order toobtain the desired gas movement at the remote end of the beam path.

Although a beam path 10 a enclosed by a bellows system is depicted, thepractice of the present invention is not necessarily limited to enclosedbeam paths. The present invention teaches and encompasses thedistribution of gas proximal to the beam path in an amount sufficient toproduce the desired gas movement within the beam path along a length ofthe beam path sufficient to produce the desired reduction, eliminationor minimization of degradation of beam quality, regardless of whether anenclosure is used with the beam delivery system. Additionally, thepresent invention may be used with a sealed beam delivery system.

Although a moving optics system has been depicted, the present inventionmay also be used with a stationary optics system.

In the depicted embodiment, a gas discharge tube is used along thelength of X axis 18 and Y axis 20, but not along Z axis 22, although itcould be. The present invention may also be practiced without a gasdischarge tube along Y axis 20, as it is believed that about seventyfive percent of the improvement in the power distribution can beachieved by using a gas discharge tube along only X axis 18. Of course,the amount of improvement depends on the amount of gas flow proximal tothe beam path. When the length of the beam path along X axis 18 issmall, such as when material is cut near field, gas discharge along Xaxis 18 has less effect than when the length of the beam path along Xaxis 18 is long, such as when material is cut far field.

Although the present invention has been described in reference to alaser beam, is may be used with any photon beam delivery system.

In summary, numerous benefits have been described which result fromemploying the concepts of the invention. The foregoing description of apreferred embodiment of the invention has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form disclosed. Obvious modificationsor variations are possible in light of the above teachings. Theembodiment was chosen and described in order to best illustrate theprinciples of the invention and its practical application to therebyenable one of ordinary skill in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto.

What is claimed is:
 1. An apparatus for cutting a target with a photonenergy beam comprising: a resonator operative to generate a photonenergy beam; a laser head operative to direct the photon energy beam toa target; a moving optics system providing a beam path opticallycoupling said resonator with said laser head, said photon energy beambeing directed by said moving optics system from said resonator to saidlaser head; and a gas distribution manifold positioned proximate to thebeam path of said moving optics system, said gas distribution manifoldhaving a plurality of spaced-apart gas outlets positioned along at leasta portion of the beam path and each of said gas outlets being configuredto deliver a flow of a gas substantially directed toward the beam path.2. The apparatus of claim 1, wherein each gas outlet is oriented suchthat the flow of the gas is discharged transverse to the beam path. 3.The apparatus of claim 2, wherein each gas outlet is oriented such thatthe flow of the gas is discharged generally perpendicular to the beampath.
 4. The apparatus of claim 1, wherein said gas distributionmanifold comprises a gas distribution tube having a tubular side walland each gas outlet extends through said tubular side wall.
 5. Theapparatus of claim 4, wherein said gas distribution tube is generallyaligned with respect to the beam path.
 6. The apparatus of claim 4,wherein said gas distribution tube is aligned substantially parallel tothe beam path.
 7. The apparatus of claim 4, wherein said gasdistribution tube is formed of a uniformly porous material.
 8. Theapparatus of claim 1, further comprising a gas source capable ofproviding said gas to said gas distribution manifold and said gasdistribution manifold includes an inlet that is fluidically coupled withsaid gas source.
 9. The apparatus of claim 8, wherein said gas source isa source of dried and filtered air and the gas is dried and filteredair.
 10. The apparatus of claim 8, wherein the flow of the gas is at aflow rate effective to reduce the degradation of the photon energy beam.11. An apparatus for cutting a target with a photon energy beamcomprising: a resonator operative to generate a photon energy beam; alaser head operative to direct the photon energy beam to a target; amoving optics system including a plurality of relatively movable mirrorsproviding a beam path optically coupling said resonator with said laserhead, said photon energy beam being directed by said mirrors from saidresonator to said laser head, and a length of said beam path changing assaid mirrors are moved relative to each other; and a gas distributiontube positioned proximate to the beam path of said moving optics system,said gas distribution having a plurality of openings spaced along atleast a portion of the beam path and each of said openings beingoriented to deliver a flow of a gas substantially directed toward thebeam path, the flow being at a flow rate effective to reduce thedegradation of a photon energy beam directed along the beam path. 12.The apparatus of claim 11, wherein each opening is oriented such thatthe flow of the gas is discharged transverse to the beam path.
 13. Theapparatus of claim 12, wherein each opening is oriented such that theflow of the gas is discharged generally perpendicular to the beam path.14. The apparatus of claim 11, wherein said gas distribution tube isgenerally aligned relative to the beam path.
 15. The apparatus of claim14, wherein said gas distribution tube is aligned substantially parallelto the beam path.
 16. The apparatus of claim 11, further comprising agas source capable of providing said gas to said gas distribution tubeand said gas distribution tube includes an inlet that is fluidicallycoupled with said gas source.
 17. The apparatus of claim 16, whereinsaid gas source is a source of dried and filtered air and said gas isdried and filtered air.
 18. A method for reducing the degradation of aphoton energy beam in a laser cutter, comprising: directing the photonenergy beam along a beam path of a moving optics system from a resonatorto a laser head; delivering a flow of a gas at a plurality of separatespaced positions along the beam path, the flow of the gas beingsubstantially directed toward the beam path at each of said separatespaced positions and the flow of the gas having a flow rate effective toreduce the degradation of the photon energy beam; and directing thephoton energy beam from the laser head to cut a target.
 19. The methodof claim 18, further comprising, before the step of delivering,filtering the gas to remove particulate matter.
 20. The method of claim18, further comprising, before the step of delivering, drying the gas.21. The method of claim 20, further comprising, before the step ofdelivering, filtering the gas to remove particulate matter.
 22. Themethod of claim 18, wherein the step of delivering further comprisesorienting the flow of the gas transverse to the beam path.
 23. Themethod of claim 22, wherein the step of delivering further comprisesorienting the flow of the gas generally perpendicular to the beam path.